1. Field of the Invention
The present invention relates to enhancing the efficiency of operation of heat exchangers and particularly to cleaning the heat transfer surfaces of a device utilized to transfer thermal energy from a flowing gas to another fluid medium. More specifically, this invention is directed to facilitation of the removal of solid matter which collects on heating surfaces, for example the evaporator or superheater heating surfaces of steam generators, that are exposed to hot gases having particulate matter entrained therein. Accordingly, the general objects of the present invention are to provide novel and improved methods of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for employment in those industrial processes where waste heat is utilized to generate steam. In such processes, a dust-laden hot gas may be directed through a steam generator for the purpose of extracting thermal energy from the gas while simultaneously cooling the gas prior to its further treatment and ultimate release to the atmosphere. The efficiency of operation of a steam generator is a direct function of the cleanliness of the heat transfer surfaces of the device. Thus, since solid matter condensed from and/or particular matter entrained in the hot waste gas and deposited on the heat exchange surfaces will seriously degrade heat transfer efficiency, provision for cleaning the steam generator must be made.
In the prior art, in order to ensure continuous steam generator operation and, consequently, as uniform a steam emission as possible, various cleaning methods have been employed. These prior art cleaning methods include:
(a) cleaning of the heating surfaces by means of blast lances; PA1 (b) ball rain cleaning; PA1 (c) knocking; PA1 (d) cleaning by shaking and/or striking; PA1 (e) sonic cleaning.
As will be briefly discussed below, all of the above-listed prior art cleaning techniques have been found to have the disadvantage of being ineffective under certain circumstances.
With respect to the use of blast lances, also referred to as sootblowing, the technique is often ineffective. This lack of effectiveness, in many cases, results from the fact that the steam generator will be employed in an environment where foreign media, for example steam, air or inert gas, cannot be blasted due to production reasons or the danger of corrosion.
The mechanical cleaning methods of techniques (b),(c),(d) and (e) above require, for operation, a mechanical impact on the surfaces to be cleaned. However, such mechanical impact will result in removal of deposits from the surface only if such deposits are dry and/or have hardened on the surface and thus are to some extent brittle. In many environments, the deposits which are formed on the steam generator heat exchange surfaces are adhesive and thus do not harden on such surfaces. These adhesive deposits, which do not harden and consequently become brittle, cannot be removed by impact or by vibration and, in time, will cause an interruption of steam generator operation.
In many cases, the temperature of the heating surface will determine whether any impurities deposited from the hot waste gas will harden on the surface, i.e., steam generator heat exchange surface temperature will determine the effectiveness of the mechanical cleaning methods. Line pressures and steam conditions in complicated, large facilities are often not freely chosen and steam pressures and steam super-heating temperatures are commonly used which result in a steam generator heat exchange surface temperature that remains above the softening point of the deposits formed thereon. Accordingly, such deposits are effectively adhesive contaminations.